1Contribution of the National Institute of Standards and Technology, an agency of the U.S. government, not subject to copyright in the U.S.

2Corresponding authors.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received March 31, 2017; final manuscript received November 13, 2017; published online December 14, 2017. Assoc. Editor: Steve J. Hensel.This work is in part a work of the U.S. Government. ASME disclaims all interest in the U.S. Government's contributions.

Abstract

A comprehensive testing program to determine the fatigue crack growth rate (FCGR) of pipeline steels in pressurized hydrogen gas was completed. Four steels were selected, two X52 and two X70 alloys. Other variables included hydrogen gas pressures of 5.5 MPa and 34 MPa, a load ratio, R, of 0.5, and cyclic loading frequencies of 1 Hz, 0.1 Hz, and 0.01 Hz. Of particular interest was whether the X70 materials would exhibit higher FCGRs than the X52 materials. The American Petroleum Institute steel designations are based on specified minimum yield strength (SMYS), and monotonic tensile tests have historically shown that loss of ductility correlates with an increase in yield strength when tested in a hydrogen environment. The X70 materials performed within the experimental spread of the X52 materials in FCGR, except for the vintage X52 material at low (5.5 MPa) pressure in hydrogen gas. This program was developed in order to provide a modification to the ASME B31.12 code that is based upon fatigue, the primary failure mechanism in pipelines. The code modification is a three-part Paris law fit of the upper bound of measurements of FCGR of pipeline steels in pressurized hydrogen gas. Fatigue crack growth data up to 21 MPa (3000 psi) are used for the upper bound. This paper describes, in detail, the testing that formed the basis for the code modification.

Quantitative equivalent grain diameter results for all four materials of this work. Statistically significant results areshown (*p < 0.05), except for X52 vintage comparison to allother materials, which was significantly different for all locations.

Conceptual drawing (a) showing the elements of the linked chain of specimens, (b) a photograph showing the assembled chain with polytetrafluoroethylene spacers, and (c) a photograph showing the assembled chain, complete with CMOD gages and aluminum spacers, ready for installation in the pressure chamber

Data showing the FCGR of two X70 specimens of the same material where one completed testing in 4 days and the other in 4 weeks, demonstrating that there is no precharging effect. Both were tested in pressurized hydrogen gas of 5.5 MPa, R = 0.5, and a cyclic loading rate of 1 Hz.

Fatigue crack growth rate with respect to cyclic loading frequency for a vintage X52 pipeline steel and a modern X52 pipeline steel at a hydrogen gas pressure of 5.5 MPa. The lines shown are visual fits to the combined data for those test conditions to better differentiate between different loading frequencies.

Fatigue crack growth rate with respect to cyclic loading frequency for vintage X52 pipeline steel and for X70A pipeline steel at a hydrogen gas pressure of 34 MPa. The lines shown are visual fits to the combined data for those test conditions to better differentiate between the different loading frequencies.

Fatigue crack growth rate data at a fixed ΔK of 14 MPa m0.5 for all four materials, both hydrogen gas pressures, and all cyclic loading frequencies for which there were completed tests. Note that X70A has a larger range of y-axis.

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